Trends in the occurrence of large Whooping Crane groups during migration in the great plains, USA

Andrew J Caven,Matt Rabbe,Jenna Malzahn,Anne E Lacy

doi:10.1016/j.heliyon.2020.e03549

Andrew J Caven, Matt Rabbe + Show 2 more

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https://doi.org/10.1016/j.heliyon.2020.e03549

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Abstract

Recent detections of large gatherings of Whooping Cranes suggest that flock sizes may be increasing at some stopover locations during both the spring and fall migrations. We used the public sightings database managed by the US Fish and Wildlife Service from 1942 to 2018 to analyze data for long-term trends in group size. We then examined the spatial distribution of large groups to explore potential explanations for these occurrences. The proportion of Whooping Crane groups comprised of 2, 3, and 4–6 individuals showed no trend over time. However, observations of individuals showed a declining trend and groups of 7–9 and ≥10 showed an increasing trend. The frequency of groups observed exceeding 5 and 10 individuals were better predicted by survey year than by Whooping Crane population size suggesting that an increasing population is not the sole driver of large group occurrences. Our results indicate that large groups occur disproportionately within the 50% migration corridor, at staging areas within the first or last 20–30% of the migration path, and near conservation-managed wetlands, particularly within the southern Great Plains. Our results suggest that in addition to population growth, conspecific attraction, location within the migration corridor, and habitat loss may be contributing to large group occurrences. Further research is needed to determine the degree to which these factors influence large Whooping Crane group formation. The gathering of large numbers of Whooping Cranes in a single location presents potential tradeoffs for the species. While increasing group sizes may improve threat detection and avoidance, it comes at a cost of increased disease and mass mortality risk.

Highlights

Whooping Cranes (Grus americana) are federally endangered, with the last remaining self-sufficient wild population of about 500 individuals migrating between wintering grounds in Aransas National Wildlife Refuge, Texas and breeding grounds in Wood Buffalo National Park, Canada (Butler and Harrell, 2018; Pearse et al, 2018a)
We provide evidence to suggest that large Whooping Crane flocks, or groupings of flocks, are more likely to occur near the center of the migration corridor
Our results suggest that large groups may form where high quality reliable wetland habitat is available in parts of the migration corridor where habitat and quality alternatives are limited

Summary

Introduction

Whooping Cranes (Grus americana) are federally endangered, with the last remaining self-sufficient wild population of about 500 individuals migrating between wintering grounds in Aransas National Wildlife Refuge, Texas and breeding grounds in Wood Buffalo National Park, Canada (Butler and Harrell, 2018; Pearse et al, 2018a). Whooping Cranes commonly migrate as individuals, pairs, families, or in small flocks (Armbruster, 1990; Kuyt, 1992; USFWS, 1994; Austin and Richert, 2001; Hefley et al, 2015). Whooping cranes are territorial and non-gregarious during the breeding season and on the wintering grounds (Erickson and Derrickson, 1981, Cottam, 1996; Chavez-Ramirez, 1996). They exhibit more gregarious behavior during migration, occasionally gathering in flocks beyond their family groups (Erickson and Derrickson, 1981; Cottam, 1996; Walkinshaw, 1996). Records of flock sizes ranging from 6 to 20 individuals have been considered noteworthy over the last century (Bent, 1963; Kuyt, 1987, 1992; Armbruster, 1990; Walkinshaw, 1996; Austin and Richert, 2001; Sharpe et al, 2001)

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